It is known to provide barrels or drums with cover and bottom members which are peripherally secured to the generally cylindrical drum body and in which at least the cover member is formed with a filling opening, an edge of which can be secured to a fitting of a tap or other closure member adapted to be used in draining or filling the drum. The cover disk can be recessed in the upper end of the drum body and the cover can be formed with a short wall portion surrounding the cover disk which is formed with the opening along the upper edge of the wall portion, the cover is secured to the upper edge of the generally cylindrical body by mechanical means, such as folding or rolling and/or by a weld seam.
In the past, the cover disk of the cover was generally planar. Such covers had the drawback that they were easily deformable, can be plastically distorted with even relatively small forces applied from the exterior and could not necessarily allow the contents of the barrel or drum to drain fully.
To overcome the tendency of a flat or planar cover disk to deform with only slight applied forces, it has been proposed for small containers such as food cans or containers for lacquers or paints, to form the cover disk or the bottom disk with circular corrugations or limited depth by an embossing process to stabilize these surfaces structurally.
For large containers, especially drums or barrels, covers with slightly convex dished disk configurations were employed to increase the resistance to deformation.
With such systems, it was found to be difficult to weld flanges, pipe fittings or the like with closures such as bungs or taps because it could not be assured that the applied fitting would always be perpendicular to the surface region in which the fitting was attached.
Indeed, with dished or domed covers provided with bungs or plugs, generally where two such plugs were provided on opposite sides of the cover, they had mutually divergent axes.
As noted, the complete emptying of barrels or drums has long been a problem. When, for example, a suction pipe connection to a pump is used, a substantial residue within the barrel could not be avoided. It has been found, in practice, that one could not even remove these residues completely by turning over a barrel and draining it from the filling opening in most cases.
In German Patent Document DE-OS No. 37 06 581, it is suggested that conventional plugs or tape applied by force-fit, welding or a screw connection not be used, but rather the barrel be provided with a fitting having a length equal to the thickness of the sheetmetal of the cover and securing it in the filling opening by the use of a laser weld seam. The tap is then applied to this element. The fitting in this case, does not project materially into the interior of the container, but rather lies flush with the inner surface thereof, by contrast with other fitting systems which project significantly into the interior of the drum, thereby allowing a relatively complete draining when the drum has been turned over.